In many communication systems (e.g., a cellular communication system, a wireless communication system, a wireless local area network, etc.), a geographic area is divided into multiple regions (e.g., cells and/or sectors of cells). In a cellular communication system, each cell is served by an access point, which can be called the NodeB, the fixed station, the cell tower, or any other appropriate term. In turn, the system users utilize mobile equipment to communicate with a fixed station. This mobile equipment can be called the user equipment (UE), the mobile station (MS), the mobile terminal (MT), the user, or any other appropriate term. Example mobile UEs include a personal digital assistant (PDA), an MP3 player such as an iPod®, a wireless telephone (e.g., a cellular phone, a voice over Internet Protocol (VoIP) phone, a smart phone, etc.), a laptop computer with wireless communication capabilities (e.g., including a wireless modem card), etc. Examples of substantially stationary UEs include any personal computer (PC) with wireless communication capabilities. Each cell is associated with a corresponding serving NodeB, where the NodeB can serve multiple cells. To improve system performance, communication resources can be re-used across cells, where the re-use can be either “fractional re-use” or “full re-use,” of communications resources. These resources can include frequencies, time-slots, signature codes, channels, reference signals, pilot signals, etc. Wireless systems, which employ a cellular re-use of communications resources, are typically called “cellular” communication systems. Transmitters and receivers can be simultaneously present in any given cell. In case of uplink (also known as “reverse link” or any other similar term) communication, transmitters are at UEs, and receivers are at NodeBs. In case of downlink (also known as “forward link” or any other similar term) communication, transmitters are at NodeB, and receivers are at the UE. In general, we will just refer to “transmitters” and “receivers.”
Communication between transmitters and receivers occurs via signals. A signal can be designated as either a) “information-bearing signal,” or alternatively, as b) a “reference signal,” Furthermore, a signal may comprise a combination of one or more information-bearing signals and/or one or more reference signals. Information-bearing signals may comprise data or control signals, or a combination thereof. Information-bearing signals carry information from the transmitter to the receiver. In contrast, a “reference signal” (RS) is a signal which is revealed to both the transmitter and the receiver a-priori, and is therefore totally known by the receiver prior to any detection or estimation process. As such, the RS can be used for estimation of the communication medium (channel). The “reference signal” can also be termed as the “pilot signal”, the “training signal,” or any other similar term. Reference signals are used for: channel estimation, channel sounding, channel quality estimation, synchronization, timing-offset estimation, frequency-offset estimation, as carriers when modulated (with data or control info), or for any other purpose. Channel estimates, which are obtained from received reference signals, are used for data demodulation. Channel quality estimates, which are also obtained from received reference signals, can be used for purposes of user scheduling, link adaptation, power control, and/or other purposes.